1. Field of Invention
The present invention relates to techniques for agglomerating mature fine tailing in a process flow, e.g., by injecting a polymer.
2. Description of Related Art
During extraction of the oil from oil sand, tailings consisting of water, silt, clays and other solvents are also typically created. When applied to oil sands mining, the term “tailings” refers specifically to fine waste suspended in water. Over time, this solid will typically become mature fine tailings (MFT) by the gravity when settling.
MFT may be processed as a rheological fluid, which may be characterized by a non-Newtownian constitutive equation. Often a Bingham model or a Herschel-Bulkley model may be applied to model the rheological behaviour of MFT.
During processing, Bingham fluids are understood to exhibit a yield point, and wall shear stresses below the yield point will not result in flow. Otherwise the shear stress increases linearly with the shear rate.
In comparison, Herschel-Bulkley fluids are also understood to exhibit a yield point but the shear stresses increase either super-linearly or supra-linearly with the shear rate. Herschel-Bulkley fluids are therefore capable of modeling dilatant or pseudo-plastic behaviour.
FIG. 1a shows a comparison of the various constitutive equations for MFT. This figure is drawn to scale and contains representative values for MFT that were used in the evaluation and development of the present invention, consistent with that set forth below. For reference, the line labeled a represents water at room temperature which is purely a Newtonian fluid.
By way of example, in order to reduce the required size of tailings ponds and in order to reclaim water, MFT may be dried and used as backfill material. Polymer induced ‘drying’ MFT is a process under development which appears to yield substantial gains over natural drying techniques or mechanical drying methods. In polymer induced drying, a polymer may be added to a stream of MFT flowing in a pipe. Under the right conditions, MFT fines will floc and be susceptible to settling. However, there is currently no known technology to monitor the state of the reacting, floccing and possibly settling of a MFT/polymer slurry. As a result, it may be difficult to adjust the polymer dosing rate to cope with natural variability in the MFT. Likewise it is a challenge to adjust the shear rate in the reacting and floccing MFT such as not to shear apart the flocs.